<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>画形</title>
</head>
<body>

    <style>
    /*三角形*/
.dialog::after{
  content: "";
  display: block;
  width:0;
  height: 0;
  border-top: 100px solid transparent;
  border-bottom:100px solid transparent;
  border-left:100px solid #ff0;
}

  </style>
  <div class="dialog"></div>
  <style>
    /*菱形*/
.diamond{
  width:100px;
  height: 100px;
  background-color: yellow;
  transform:rotate(-45deg)
}
.diamond2{
  width:100px;
  height: 50px;
  background-color: yellow;
  transform:skew(20deg,0deg);
}
  </style>
  <div class="diamond"></div>
  <div class="diamond2"></div>

  <hr>
<style>
  #star-five {
    margin: 60px 0;
    position: absolute;
    display: block;
    color: red;
    width: 0;
    height: 0;
    border-right: 100px solid transparent;
    border-bottom: 70px solid red;
    border-left: 100px solid transparent;
    transform: rotate(35deg);
    left: 200px;
  }

  #star-five:before {
    border-bottom: 80px solid red;
    border-left: 30px solid transparent;
    border-right: 30px solid transparent;
    position: absolute;
    height: 0;
    width: 0;
    top: -45px;
    left: -65px;
    display: block;
    content: '';
    transform: rotate(-35deg);
  }

  #star-five:after {
    position: absolute;
    display: block;
    color: red;
    top: 3px;
    left: -105px;
    width: 0px;
    height: 0px;
    border-right: 100px solid transparent;
    border-bottom: 70px solid red;
    border-left: 100px solid transparent;
    transform: rotate(-70deg);
    content: '';
  }
</style>
<div id="star-five"></div>
<div style="height: 100px;"></div>
<style>
#star-six{
  width:0px;height:0px;
  border-bottom:100px solid red;
  /*rgba(244,244,0,0.4);*/
  border-left:50px solid transparent;
  border-right:50px solid transparent;
  margin:50px auto;
  position:relative;
}
#star-six:after{
  content:" ";
  width:0px;height:0px;
  border-top:100px solid red;
  /*rgba(0,244,250,0.6);*/
  border-left:50px solid transparent;
  border-right:50px solid transparent;
  position:absolute;
  top:50px;left:-50px;
}
</style>
<div id="star-six"></div>
</body>
</html>